This invention relates to methods of recycling catalyst, and more specifically it relates to methods of exchanging solvents in a solution of catalyst, produced after oxidation of cyclohexane to adipic acid, in a manner to render the catalyst beneficially recyclable to the beginning of the oxidation process.
There is a plethora of references (both patents and literature articles) dealing with the formation of acids, one of the most important being adipic acid, by oxidation of hydrocarbons. Adipic acid is used to produce Nylon 66 fibers and resins, polyesters, polyurethanes, and miscellaneous other compounds.
There are different processes of manufacturing adipic acid. The conventional process involves a first step of oxidizing cyclohexane with oxygen to a mixture of cyclohexanone and cyclohexanol (KA mixture), and then oxidation of the KA mixture with nitric acid to adipic acid. Other processes include, among others, the xe2x80x9cHydroperoxide Process,xe2x80x9d the xe2x80x9cBoric Acid Process,xe2x80x9d and the xe2x80x9cDirect Synthesis Process,xe2x80x9d which involves direct oxidation of cyclohexane to adipic acid with oxygen in the presence of solvents, catalysts, and promoters.
The Direct Synthesis Process has been given attention for a long time. However, to this date it has found little commercial success. One of the reasons is that although it looks very simple at first glance, it is extremely complex in reality. Due to this complexity, one can find strikingly conflicting results, comments, and views in different references.
It is well known that after a reaction has taken place according to the Direct Synthesis, a mixture of two liquid phases is present at ambient temperature, along with a solid phase mainly consisting of adipic acid. The two liquid phases have been called the xe2x80x9cPolar Phasexe2x80x9d and the xe2x80x9cNon-Polar Phase.xe2x80x9d However, no attention has been paid so far to the importance of the two phases, except for separating the adipic from the xe2x80x9cPolar Phasexe2x80x9d and recycling these phases to the reactor partially or totally with or without further treatment.
It is also important to note that most studies on the Direct Synthesisxe2x80x94have been conducted in a batch mode, literally or for all practical purposes.
As aforementioned, there is a plethora of references dealing with oxidation of organic compounds to produce acids, such as, for example, adipic acid and/or intermediate products, such as for example cyclohexanone, cyclohexanol, cyclohexylhydroperoxide, etc.
The following references, among others, may be considered as representative of oxidation processes relative to the preparation of diacids and other intermediate oxidation products.
U.S. Pat. No. 5,463,119 (Kollar) discloses a process for the oxidative preparation of C5-C8 aliphatic dibasic acids by
(1) reacting,
(a) at least one saturated cycloaliphatic hydrocarbon having from 5 to 8 ring carbon atoms in the liquid phase and
(b) an excess of oxygen gas or an oxygen-containing gas in the presence of
(c) a solvent comprising an organic acid containing only primary and/or secondary hydrogen atoms and
(d) at least about 0.002 mole per 1000 grams of reaction mixture of a polyvalent heavy metal catalyst;
(2) removing the aliphatic dibasic acid; and
(3) recycling intermediates, post oxidation components, and derivatives thereof remaining after removal of the aliphatic dibasic acid into the oxidation reaction.
U.S. Pat. No. 5,374,767 (Drinkard et al.) discloses formation of cyclohexyladipates in a staged reactor, e.g., a reactive distillation column. A mixture containing a major amount of benzene and a minor amount of cyclohexene is fed to the lower portion of the reaction zone and adipic acid is fed to the upper portion of the reaction zone, cyclohexyladipates are formed and removed from the lower portion of the reaction zone and benzene is removed from the upper portion of the reaction zone. The reaction zone also contains an acid catalyst.
U.S. Pat. No. 5,321,157 (Kollar) discloses a process for the preparation of C5-C8 aliphatic dibasic acids through oxidation of corresponding saturated cycloaliphatic hydrocarbons by
(1) reacting, at a cycloaliphatic hydrocarbon conversion level of between about 7% and about 30%,
(a) at least one saturated cycloaliphatic hydrocarbon having from 5 to 8 ring carbon atoms in the liquid phase and
(b) an excess of oxygen gas or an oxygen containing gas mixture in the presence of less than 1.5 moles of a solvent per mole of cycloaliphatic hydrocarbon (a), wherein said solvent comprises an organic acid containing only primary and/or secondary hydrogen atoms and
(d) at least about 0.002 mole per 1000 grams of reaction mixture of a polyvalent heavy metal catalyst; and
(2) isolating the C5-C8 aliphatic dibasic acid.
U.S. Pat. No. 3,987,100 (Barnette et al.) describes a process of oxidizing cyclohexane to produce cyclohexanone and cyclohexanol, said process comprising contacting a stream of liquid cyclohexane with oxygen in each of at least three successive oxidation stages by introducing into each stage a mixture of gases comprising molecular oxygen and an inert gas.
U.S. Pat. No. 3,957,876 (Rapoport et al.) describes a process for the preparation of cyclohexyl hydroperoxide substantially free of other peroxides by oxidation of cyclohexane containing a cyclohexane soluble cobalt salt in a zoned oxidation process in which an oxygen containing gas is fed to each zone in the oxidation section in an amount in excess of that which will react under the conditions of that zone.
U.S. Pat. No. 3,932,513 (Russell) discloses the oxidation of cyclohexane with molecular oxygen in a series of reaction zones, with vaporization of cyclohexane from the last reactor effluent and parallel distribution of this cyclohexane vapor among the series of reaction zones.
U.S. Pat. No. 3,530,185 (Pugi) discloses a process for manufacturing precursors of adipic acid by oxidation with an oxygen-containing inert gas which process is conducted in at least three successive oxidation stages by passing a stream of liquid cyclohexane maintained at a temperature in the range of 140xc2x0 C. to 200xc2x0 C. and a pressure in the range of 50 to 350 p.s.i.g. through each successive oxidation stage and by introducing a mixture of gases containing oxygen in each oxidation stage in an amount such that substantially all of the oxygen introduced into each stage is consumed in that stage thereafter causing the residual inert gases to pass countercurrent into the stream of liquid during the passage of the stream through said stages.
U.S. Pat. No. 3,515,751 (Oberster et al.) discloses a process for the production of epsilon-hydroxycaproic acid in which cyclohexane is oxidized by liquid phase air oxidation in the presence of a catalytic amount of a lower aliphatic carboxylic acid and a catalytic amount of a peroxide under certain reaction conditions so that most of the oxidation products are found in a second, heavy liquid layer, and are directed to the production of epsilon-hydroxycaproic acid.
U.S. Pat. No. 3,361,806 (Lidov et al.) discloses a process for the production of adipic acid by the further oxidation of the products of oxidation of cyclohexane after separation of cyclohexane from the oxidation mixture, and more particularly to stage wise oxidation of the cyclohexane to give high yields of adipic acid precursors and also to provide a low enough concentration of oxygen in the vent gas so that the latter is not a combustible mixture.
U.S. Pat. No. 3,234,271 (Barker et al.) discloses a process for the production of adipic acid by the two-step oxidation of cyclohexane with oxygen. In a preferred embodiment, mixtures comprising cyclohexanone and cyclohexanol are oxidized. In another embodiment, the process involves the production of adipic acid from cyclohexane by oxidation thereof, separation of cyclohexane from the oxidation mixture and recycle thereof, and further oxidation of the other products of oxidation.
U.S. Pat. No. 3,231,608 (Kollar) discloses a process for the preparation of aliphatic dibasic acids from saturated cyclic hydrocarbons having from 4 to 8 cyclic carbon atoms per molecule in the presence of a solvent which comprises an aliphatic monobasic acid which contains only primary and secondary hydrogen atoms and a catalyst comprising a cobalt salt of an organic acid, and in which process the molar ratio of said solvent to said saturated cyclic hydrocarbon is between 1.5:1 and 7:1, and in which process the molar ratio of said catalyst to said saturated cyclic hydrocarbon is at least 5 millimoles per mole.
U.S. Pat. No. 3,161,603 (Leyshon et al.) discloses a process for recovering the copper-vanadium catalyst from the waste liquors obtained in the manufacture of adipic acid by the nitric acid oxidation of cyclohexanol and/or cyclohexanone.
U.S. Pat. No. 2,565,087 (Porter et al.) discloses the oxidation of cycloaliphatic hydrocarbons in the liquid phase with a gas containing molecular oxygen and in the presence of about 10% water to produce two phases and avoid formation of esters.
U.S. Pat. No. 2,557,282 (Hamblet et al.) discloses production of adipic acid and related aliphatic dibasic acids; more particularly to the production of adipic acid by the direct oxidation of cyclohexane.
U.S. Pat. No. 2,439,513 (Hamblet et al.) discloses the production of adipic acid and related aliphatic dibasic acids and more particularly to the production of adipic acid by the oxidation of cyclohexane.
U.S. Pat. No. 2,223,494 (Loder et al.) discloses the oxidation of cyclic saturated hydrocarbons and more particularly to the production of cyclic alcohols and cyclic ketones by oxidation of cyclic saturated hydrocarbons with an oxygen-containing gas.
U.S. Pat. No. 2,223,493 (Loder et al.) discloses the production of aliphatic dibasic acids and more particularly to the production of aliphatic dibasic acids by oxidation of cyclic saturated hydrocarbons with an oxygen-containing gas.
German Patent DE 44 26 132 A1 (Kysela et al.) discloses a method of dehydration of process acetic acid from liquid -phase oxidation of cyclohexane with air, in the presence of cobalt salts as a catalyst after separation of the adipic acid after filtration, while simultaneously avoiding cobalt salt precipitates in the dehydration column, characterized in that the acetic acid phase to be returned to the beginning of the process is subjected to azeotropic distillation by the use of added cyclohexane, under distillative removal of the water down to a residual content of less than [sic] 0.3-0.7%.
PCT International Publication WO 96/03365 (Costantini et al.) and U.S. Pat. No. 5,756,837 (Costantini et al.) disclose a process for recycling a cobalt-containing catalyst in a direct reaction of oxidation of cyclohexane into adipic acid, characterized by including a step in which the reaction mixture obtained by oxidation into adipic acid is treated by extraction of at least a portion of the glutaric acid and the succinic acid formed during the reaction.
The patent literature is inconsistent and at least confusing regarding addition or removal of water in oxidations. For example:
U.S. Pat. No. 5,221,800 (Park et al.) discloses a process for the manufacture of adipic acid. In this process, cyclohexane is oxidized in an aliphatic monobasic acid solvent in the presence of a soluble cobalt salt wherein water is continuously or intermittently added to the reaction system after the initiation of oxidation of cyclohexane as indicated by a suitable means of detection, and wherein the reaction is conducted at a temperature of about 50xc2x0 C. to about 150xc2x0 C. at an oxygen partial pressure of about 50 to 420 pounds per square inch absolute.
U.S. Pat. No. 4,263,453 (Schultz et al.) discloses a process claiming improved yields by the addition of water at the beginning of the reaction, generally of the order of 0.5 to 15% relative to monobasic aliphatic acid solvent, and preferably 1 to 10% relative to the solvent.
U.S. Pat. No. 3,390,174 (Schultz et al.) discloses a process claiming improved yields of aliphatic dibasic acids when oxidizing the respective cyclic hydrocarbons at temperatures between 130xc2x0 C. and 160xc2x0 C., while removing the water of reaction substantially as quickly as it is formed.
None of the above references, or any other references known to the inventors disclose, suggest or imply, singly or in combination, catalyst treatment for recycling subject to the intricate and critical controls and requirements of the instant invention as described and claimed.
Our U.S. Pat. Nos. 5,654,475, 5,580,531, 5,558,842, 5,502,245, 5,801,282, and co-pending application 08/587,967, filed on Jan. 17, 1996 (now U.S. Pat. No. 5,883,292, issued Mar. 16, 1999), all of which are incorporated herein by reference, describe methods and apparatuses relative to controlling reactions in atomized liquids. In addition, our U.S. Pat. Nos. 5,801,273 and 5,817,868, and the following co-pending U.S. applications are also incorporated herein by reference: 08/812,847, filed on Mar. 6, 1997; 08/824,992, filed on Mar. 27, 1997 (now U.S. Pat. No. 5,922,908, issued Jul. 13, 1999); 08/861,281 filed on May 21, 1997; 08/861,180 filed on May 21, 1997 (now allowed) 08/861,176 filed on May 21, 1997 (now U.S. Pat. No. 5,824,819, issued Oct. 20, 1998); 08/861,210 filed on May 21, 1997 (now abandoned); 08/876,692, filed on Jun. 16, 1997; 08/900,323, filed on Jul. 25, 1997 (now U.S. Pat. No. 6,037,491, issued Mar. 14, 200); 08/931,035, filed on Sep. 16, 1997 (now abandoned); 08/932,875 (now U.S. Pat. No. 6,039,902, issued Mar. 21, 2000) filed on Sep. 18, 1997; 08/934,253, filed on Sep. 19, 1997 (now U.S. Pat. No. 5,929,277, issued Jul. 27, 1999); 08/986,505 (now U.S. Pat. No. 5,908,589, issued Jun. 1, 1999), filed on Dec. 8, 1997; 08/989,910, filed on Dec. 12, 1997; 60/074,068, filed on Feb. 9, 1998; 60/075,257, filed Feb. 19, 1998; 60/086,159, filed May 20, 1998; 60/086,119, filed May 20, 1998; 60/086,118, filed May 20, 1998; 60/091,483, filed on Jul. 2, 1998; 60/091,796, filed Jul. 6, 1998; 60/093,256, filed Jul. 17, 1998; 60/105,048, filed Oct. 20, 1998; 60/101,918, filed on Nov. 24, 1998; 60/110,206, filed on Nov. 30, 1998; 60/111,848, filed Dec. 11, 1998; 60/121,170, filed Feb. 22, 1999; and 60/122,705, filed Mar. 3, 1999.
As aforementioned, this invention relates to methods of exchanging solvents in a solution of catalyst, produced after oxidation of cyclohexane to adipic acid, in a manner to render the catalyst beneficially recyclable to the beginning of the oxidation process. More specifically, this invention relates to a method of replacing water and cyclohexanone with acetic acid in an aqueous solution of a metal catalyst, the solution having been produced after oxidation of cyclohexane to adipic acid, the method comprising steps of:
(a) feeding the aqueous solution of the metal catalyst to a top plate or an intermediate plate of a solvent exchange column, the solvent exchange column also having a bottom plate;
(b) removing a bottoms liquid from the vicinity of the bottom plate, the bottoms liquid being at a bottoms temperature;
(c) boiling the bottoms liquid in a re-boiler and returning produced bottoms vapors to the column in the vicinity of the bottom plate:
(d) introducing acetic acid to the re-boiler; and
(e) removing from the re-boiler an acetic acid solution of the metal catalyst comprising no substantial amounts of water and cyclohexanone.
The method of the instant invention may further comprise steps of removing top vapors from the vicinity of the top plate of the solvent exchange column, condensing said vapors to form a condensate, and, if the condensate constitutes two liquid phases, separating said condensate into an upper liquid phase comprising a majority of cyclohexanone, and a lower liquid phase comprising a majority of water.
Preferably, the metal catalyst comprises a cobalt compound.
In addition, the method may further comprise a step of adding water to either the re-boiler, or to the solvent exchange column, or to both.
The water content in the bottoms liquid may be controlled and maintained at a level higher than that under which metal catalyst precipitates at or over the bottoms temperature. The water content may be further controlled, preferably in a manner to still remain low enough to be suitable for recycling to a reaction chamber of the oxidation of cyclohexane to adipic acid without formation of a second liquid phase.
It is also preferable that the majority of the cyclohexanone and at least part of the water are removed before the catalyst extract enters the solvent exchange column.
A condensate formed on top of the solvent exchange column may be at least partially recycled to said exchange column.
The temperature of the column, including the bottoms temperature, may be controlled and lowered by reducing the pressure within the column by techniques well known to the art, such as use of vacuum pumps for example. The control of the temperature may be necessitated to prevent catalyst precipitation at the water levels prevailing at the vicinity of the bottom plate or the re-boiler loop.
The methods of the present invention may further comprise a step of reacting the adipic acid produced with a reactant selected from a group consisting of a polyol, a polyamine, and a polyamide in a manner to form a polymer of a polyester, or a polyamide, or a (polyimide and/or polyamideimide), respectively. These methods may also comprise a step of spinning the polymer into fibers or mixing the polymer with fillers and/or other additives to form composites.
xe2x80x9cMajorxe2x80x9d and xe2x80x9cmajorityxe2x80x9d regarding a moiety mean more than 50%, and up to substantially 100%, of said moiety by weight.
xe2x80x9cMinorxe2x80x9d and xe2x80x9cminorityxe2x80x9d regarding a moiety mean less than 50%, and down to 0%, of said moiety by weight.
xe2x80x9cIntermediate platexe2x80x9d is any plate between the top plate and the bottom plate.